We are pursuing research on the mechanism of action of drugs which affect the adrenergic nervous system and the circulation. Specifically, we are investigating the effects of recently identified metabolities of propranolol on: A) renin and renin control mechanisms; and B) cardiac his-purkinje and cardiac muscle cells. Intact animals, perfused kidneys, and renal cell suspensions are used for studies of renin. Cardiac conductile tissue is studied with microelectrodes placed in isolated canine false tendons.